Engine stall and distortion suppression system

ABSTRACT

A method is provided for equalizing fluid pressure in a primary fluid flow region, comprised of providing a modulating fluid flow region adjacent to the primary flow region and separating the two regions with a perforated wall. By controlling the fluid pressure in the modulating fluid flow region, and permitting fluid to flow between the perforated wall, the fluid pressure in the primary fluid flow region is equalized. The perforations may be formed either in at least one ring about the perimeter of the plenum or at least one row along the longitudinal direction of the plenum. Furthermore, at least one of the perforations may be canted in either the longitudinal or radial directions. This method is important in equalizing the air pressure in a turbine engine air inlet and thereby avoiding aerodynamic distortions in said inlet. Additionally, an apparatus is provided for equalizing the pressure in a primary fluid flow region.

FIELD OF THE INVENTION

The present invention relates to a novel apparatus for causing pressureequalization between flow masses in two regions, and a method forachieving said equalization. The apparatus utilizes a wall or surfacebetween the flow masses, said surface containing a plurality ofperforations, and achieves equalization by the exchange of flows throughthe perforations.

BACKGROUND

The need to equalize fluid flow in a given region is well known. Theterm “fluid” in this instance may refer to air, gas, or liquid. One ofthe most important applications of equalizing flow is in the area ofturbine engines to diminish flow distortions or the occurrence ofcompressor surge and rotating stall.

Gas turbine engines require high performance and high reliability inorder to assure that flights can be completed effectively, efficientlyand safely. This is especially true in military applications. Air isforced through the inlet or mouth of a turbine engine and from theredirected into a compressor. As the flow in the compressor is reduced ormade non-uniform while the compressor or rotational speed is heldconstant, a point will be reached at which some or all of the engineblades begin to stall and engine instabilities occur. The most violentof these is “surge”, which for high speed compressors (as in a turbineengine) can result in periodically reversed flow and mechanical damage.The other result of air being reduced or made non-uniform is rotatingstall. “Stall” can result in a region of blocked flow covering half ofthe circumference of the engine inlet and rotating at half the rotorspeed, and may lock the engine.

When a gas turbine engine experiences a compressor “stall” or “surge”,the given flight will be effected. In cases of severe surge, the engineor drive train components can fail, causing loss of engine operation.When this happens in flight, the results can be catastrophic. Similarly,a rotating “stall” can lock or freeze an engine resulting in loss ofoperation. For an in depth discussion of how a turbine engine works, andturbine engine surge and stall, see Emmons, H. W., Pearson, C. E., andGrant, H. P.; “Compressor Surge and Stall Propagation,” Transactions ofthe ASME, May, 1955, p. 455-469; and Greitzer, E. M., “The Stability ofPumping Systems—the 1980 Freeman Scholar Lecture,” ASME J. of FluidsEngineering, June, 1981, vol. 103, p. 193-242.

Surge and stall are commonly caused by: (1) engine deterioration; (2)aerodynamic distortions (especially at the air inlet); and (3) hot gasinjection (from weapon firing). Despite the knowledge of these causes,there has been little success in providing turbine engines with anyreliable way of preventing engine surge or stall.

The present invention addresses cause number (2), and teaches a way tocreate a flow of air into a turbine engine which is uniform in pressurearound the circumference of the engine inlet. As air enters an engineinlet, any variations in pressure at different points around thecircumference of the inlet create aerodynamic disturbances andmechanical stress, hence inefficiencies in the engine. If the introducedair is non-uniform in pressure, the stress on the blades of the enginewill also be non-uniform, because the blades of a turbine engine arerotating and acting on the introduced air. This stress on the enginecauses blade shape deformation, which may further deteriorate the engineand cause the engine to run inefficiently. Uniform pressure around aturbine engine inlet will assure that the flow of air into the engine isconstant and uniform, and will reduce engine stress while increasingengine efficiency.

Accordingly, an object of the present invention is to provide anapparatus that may cause fluid pressure in one region to equalize withthe pressure in another region.

It is a further object of the present invention to provide an apparatusfor equalizing the pressure of air around the inlet duct of a turbineengine.

Still another object of the present invention is to provide a method forequalizing the pressure of air around the inlet duct of a turbineengine.

All publications and references cited herein are hereby incorporatedinto this specification by reference thereto.

SUMMARY OF THE INVENTION

In accordance with these and other objects of the present invention, anapparatus is provided comprised of a means for detecting and regulatingthe pressure in a first flow area, said first flow area separated froman adjacent second flow area by a surface or wall containing a pluralityof perforations. A method for regulating the fluid pressure in saidsecond flow area is also provided, said method comprised of controllablyregulating the fluid pressure in said first flow area and permittingfluid to freely flow between said flow areas through said perforationsin said surface or wall.

This apparatus and method provides a simple and efficient means toassure pressure equalization in the air around the circumference of theinlet duct of a turbine engine, and thereby reduce or eliminateaerodynamic distortions at said inlet duct.

The novel features that are considered characteristic of the inventionare set forth with particularity in the appended claims. The inventionitself, however, both as to its structure and its operation togetherwith the additional object and advantages thereof will best beunderstood from the following description of the preferred embodiment ofthe present invention when read in conjunction with the accompanyingdrawings. Unless specifically noted, it is intended that the words andphrases in the specification and claims be given the ordinary andaccustomed meaning to those of ordinary skill in the applicable art orarts. If any other meaning is intended, the specification willspecifically state that a special meaning is being applied to a word orphrase. Likewise, the use of the words “function” or “means” in theDescription of Preferred Embodiments is not intended to indicate adesire to invoke the special provision of 35 U.S.C. §112, paragraph 6 todefine the invention. To the contrary, if the provisions of 35 U.S.C.§112, paragraph 6, are sought to be invoked to define the invention(s),the claims will specifically state the phrases “means for” or “step for”and a function, without also reciting in such phrases any structure,material, or act in support of the function. Even when the claims recitea “means for” or “step for” performing a function, if they also reciteany structure, material or acts in support of that means of step, thenthe intention is not to invoke the provisions of 35 U.S.C. §112,paragraph 6. Moreover, even if the provisions of 35 U.S.C. §112,paragraph 6, are invoked to define the inventions, it is intended thatthe inventions not be limited only to the specific structure, materialor acts that are described in the preferred embodiments, but inaddition, include any and all structures, materials or acts that performthe claimed function, along with any and all known or later-developedequivalent structures, materials or acts for performing the claimedfunction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simple plan view of a perforated surface or wall of thepresent invention.

FIG. 2 is a more detailed view of a first flow area and a second flowarea of the present invention.

FIG. 3 is a partial exploded view of a turbine engine showing the inletduct area.

FIG. 4 is a cross sectional view of an air plenum surrounding the inletof a turbine engine.

FIG. 5A is a sectional side view of an inlet duct of a turbine engineincorporating an embodiment of the present invention.

FIG. 5B is a diagram depicting a turbine engine inlet duct incorporatingthe present invention.

FIGS. 6A and 6B are illustrations of a plenum with rings ofperforations.

FIGS. 7A and 7B are illustration of a plenum with lines of perforations.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention relates to affecting the fluid pressure in oneregion by selectively controlling the fluid pressure in anotheradjoining region, said regions separated by a perforated surface orwall. The concept of the present invention is best illustrated in FIG. 1and FIG. 2. FIG. 1 shows two fluid flow areas—region 1 is the flow ofinterest (i.e., the region which is to be acted upon) called the primaryflow region, and region 2 is the flow for modulation purposes (i.e., theregion which may be controlled to affect the pressure in the primaryflow region) called the modulating flow region. Both primary flow region1 and modulating flow region 2 are occupied by a common fluid, saidfluid either liquid, gas or air.

Surface (or wall) 3 separates primary flow region 1 and modulating flowregion 2. Surface 3 is provided with at least one, preferably equally aplurality, of perforations 6. Said perforations 6 may be comprised ofsmall holes or slits, said holes or slits capable of permitting fluidflow between primary flow region 1 and modulating flow region 2.

Referring to FIG. 2, equalization of pressure between primary flowregion 1 and modulating flow region 2 is achieved by the exchange offlows through perforations 6 in perforated surface 3. Pressure inmodulating flow region 2 is actively controlled by valve 4 (which may beconnected to an external high pressure flow source 5), allowingmodulating flow region 2 to act as a constant pressure reservoir. Onemay then affect the fluid pressure in primary flow region 1 bycontrolling the fluid pressure in modulating flow region 2. Fluid masswill flow into primary flow region 1 near a perforation 6 where thepressure in modulating flow region 2 is greater than that in primaryflow region 1. In contrast, fluid mass will flow from primary flowregion 1 into modulating flow region 2 near a perforation 6 where thepressure in modulating flow region 2 is less than that in primary flowregion 1. If one provides a constant pressure throughout modulating flowregion 2, fluid will either enter or exit primary flow region 1 throughperforations 6 (depending on the pressure differences between region 1and region 2 at any given perforation 6) until an equal pressure isachieved in primary flow region 1.

This method of achieving an equal measure of pressure throughout primaryregion 1 is one way in which to address the problem of turbine enginestall or surge discussed above. One cause of turbine engine surge orstall is aerodynamic distortions (especially at the air inlet). Thesedistortions are characterized by air pressure differences in the areasurrounding the air inlet of a turbine engine. FIG. 3 shows a partialexploded view of a turbine engine, and specifically air inlet 7. Airinlet 7 is formed by the outer casing (or wall) 8 of the turbine engineand an inner barrier 9. Outer casing 8 and inner barrier 9 form airinlet 7, through which air flows into compressors 10 of the engine. Itis in this air inlet 7 that, if the pressure around the circumference ofthe inlet is not equal, aerodynamic distortions may occur and causeengine surge or stall. This is because the air entering the compressors10 of the engine is not equal in pressure and will exert unequal forceson the compressor blades. This not only decreases engine performance andreliability, but also decreases engine and fuel efficiency. By using themethod of the present invention, one may equalize the pressure of theair entering through inlet 7 and thereby increase engine efficiency anddecrease the probability of engine surge or stall.

FIG. 5B shows a simplified diagram of one application of the presentinvention to the air inlet on a turbine engine. Inlet 7 flow distortionsmay be suppressed by wrapping pressure modulating plenum 11 around airinlet 7 of a turbine engine. Pressure modulating plenum 11 formsmodulating flow region 2 described above. Primary flow region 1, asapplied to the turbine engine, is actually the flow of air into airinlet 7. This plenum may be a hollow annulus surrounding air inlet 7.Pressure modulating plenum 11 is adjacent to, and may be contiguouswith, air inlet 7.

Pressure modulating plenum 11, surrounding air inlet 7, is provided witha means for permitting flow between the interior of pressure modulatingplenum 11 and the air flowing through air inlet 7. This means may be inthe form of perforations through a common wall shared by pressuremodulating plenum 11 and air inlet 7. Referring back to FIG. 3, and toFIG. 4, said pressure modulating plenum 11 may be provided surroundingair inlet 7 exterior of outer wall 8. Outer wall 8 may act as a commonwall for air inlet 7 and pressure modulating plenum 11, withperforations provided in outer wall 8 to provided fluid (air) flowbetween pressure modulating plenum 11 and air inlet 7.

The interior space 14 (FIG. 5A) of pressure modulating plenum 11 isprovided with at least one plenum pressure sensor 15 to monitor thepressure inside plenum 11. For example, a static pressure sensor used atthe inlet of most aircraft engines may be utilized in the presentinvention. Ideally, a plurality of pressure sensors 15 are provideddispersed around the interior of plenum 11 at varying intervals tomeasure the pressure around plenum 11.

The air pressure of interior space 14 of pressure modulating plenum 11is actively controlled by a means for providing high pressure fluid flowinto pressure modulating plenum 11, or relieving the pressure in plenum11 by discharging fluid out of plenum 11. Said means for high-pressurefluid may be a regulating valve 12 capable of regulating airflow from asource of high-pressure air (e.g., from a compressor or from theinterior space of a turbine engine). Valve 12 is connected to pressuresensors 15 via a means to permit communication between the two.Therefore, if pressure sensor 15 detects a drop in pressure in plenum11, a message is sent to valve 12 to permit introduction ofhigh-pressure air into pressure modulating plenum 11. Conversely, ifpressure sensor 15 detects an increase in pressure in plenum 11, amessage is sent to valve 12 to permit discharge of air out of modulatingplenum 11.

The pressure inside pressure modulating plenum 11 is controlled to avalue approximately equal to the averaged value of the measured airflowpressures at a number of locations in inlet duct 7. The air pressure maybe determined at several locations around air inlet 7 and averaged todetermine the average air pressure entering a turbine engine. Thispressure would then be the pressure actively kept in pressure modulatingplenum 11.

FIG. 5A depicts a side view of a portion of air inlet 7. Air flowsthrough inlet 7 as shown. Surrounding air inlet 7 is pressure modulatingplenum 11, separated from inlet 7 by a perforated wall 16. The interior14 of plenum 11 is maintained at a constant pressure P, which is theaverage of measured airflow pressures at a number of locations aroundinlet 7. As air flows into air inlet 7, if the pressure of the air islower than that in pressure modulating plenum 11, air will flow out ofpressure modulating plenum 11 through perforated wall 16 and into theair flow. If the air flowing into air inlet 7 is greater than that inpressure modulating plenum 11, air will flow through perforated wall 16and into plenum 11. This way, the air pressure of the air entering inlet7 will be maintained as closely as possible to the air pressuremaintained in plenum 11, and will reduce any aerodynamic distortionsaround the circumference of air inlet 7. This will reduce or eliminatethe occurrence of turbine engine surge or stall.

While the perforations 6 may be placed in any position on the perforatedsurface 3, in one embodiment the perforations equally and radiallyspaced about the longitudinal axis of plenum 11, as illustrated in FIG.6, thereby forming at least one ring of perforations 6. In thisembodiment, it is preferred that there are more than one ring ofperforations 6, with the multiple rings equally spaced apart andlongitudinally separated. The multiple rings of perforations 6 may besituated such that the perforations 6 in adjacent rings are eitherlongitudinally aligned or slightly rotated such that the perforations 6in adjacent rings form diagonals with respect to the longitudinal axis.

In another embodiment, the perforations 6 may be placed in at least onelongitudinally aligned row, as illustrated in FIG. 7, thereby forming atleast one line of perforations 6. In this embodiment, it is preferredthat there are more than one line of perforations 6, with the multiplelines equally spaced apart and radially separated. The multiple lines ofperforations 6 may be situated such that the perforations 6 in adjacentlines are either radially aligned and form rings about the radial axisor slightly off-set in the longitudinal direction such that theperforations 6 in adjacent lines form diagonals with respect to thelongitudinal axis. Multiple lines are preferred, with a preferredminimum being between four and eight lines.

It can easily be seen that the two embodiments described above quicklybecome the same as the number of rings or lines is increased.

Additionally, it is preferred that the perforations 6 should be cantedsuch that air flow into or out of the perforations is eitherlongitudinally, such along or against the direction of the airflow, orradially, such as directed along the curvature of the plenum 11; insteadof perpendicular to air flow as would be the case with perpendicularlyaligned perforations 6. (Herein the term perpendicular meansperpendicular to the longitudinal axis of the plenum 11.) The canting ofthe perforations 6 can be either uniform in one direction or it can bealternating such that adjacent lines of perforations 6 or rings ofperforations 6 are canted in alternate radial or longitudinaldirections. This would allow the fluid to flow into one directed set ofperforations 6 and out of the other directed set of perforations 6. Itis preferred, at the time of application, that the canting be directedin the longitudinal direction and directed along the air flow direction.

The preferred embodiment of the invention is described above in theDrawings and Description of Preferred Embodiments. While thesedescriptions directly describe the above embodiments, it is understoodthat those skilled in the art may conceive modifications and/orvariations to the specific embodiments shown and described herein. Anysuch modifications or variations that fall within the purview of thisdescription are intended to be included therein as well. Unlessspecifically noted, it is the intention of the inventor that the wordsand phrases in the specification and claims be given the ordinary andaccustomed meanings to those of ordinary skill in the applicable art(s).The foregoing description of a preferred embodiment and best mode of theinvention known to the applicant at the time of filing the applicationhas been presented and is intended for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise form disclosed, and many modifications andvariations are possible in the light of the above teachings. Theembodiment was chosen and described in order to best explain theprinciples of the invention and its practical application and to enableothers skilled in the art to best utilize the invention in variousembodiments and with various modifications as are suited to theparticular use contemplated.

What is claimed is:
 1. A method of equalizing the air pressure in aturbine engine air inlet, said method comprised of: a) providing amodulating plenum adjacent to and surrounding said turbine engine airinlet, said plenum filled with air; b) separating said modulating plenumfrom said turbine engine air inlet with a wall; c) providing the wallwith a plurality of perforations, wherein at least one of theperforation is canted longitudinally, for permitting air flow betweensaid modulating plenum and said turbine engine air inlet the pluralityof perforations further being circumferentially spaced about alongitudinal axis of said plenum thus forming at least one ring ofperforations; d) regulating pressure of the air in said modulatingplenum, e) providing at least one air pressure sensor in said modulatingplenum to monitor the pressure inside said plenum; and f) maintainingthe air pressure in said modulating plenum at a determined pressure. 2.The method of claim 1 wherein at least one ring of perforations iscanted longitudinally.
 3. The method of claim 2 wherein all rings ofperforations are canted longitudinally.
 4. A method of equalizing theair pressure in a turbine engine air inlet, said method comprised of: a)providing a modulating plenum adjacent to and surrounding said turbineengine air inlet, said plenum filled with air; b) separating saidmodulating plenum from said turbine engine air inlet with a wall; c)providing the wall with a plurality of perforations, wherein at leastone perforation is canted radially, for permitting air flow between saidmodulating plenum and said turbine engine air inlet the plurality ofperforations further being circumferentially spaced about a longitudinalaxis of said plenum thus forming at least one ring of perforations; d)regulating pressure of the air in said modulating plenum, e) providingat least one air pressure sensor in said modulating plenum to monitorthe pressure inside said plenum; and f) maintaining the air pressure insaid modulating plenum at a determined pressure.
 5. The method of claim4 wherein at least one ring of perforations is canted longitudinally. 6.The method of claim 5 wherein all rings of perforations are cantedlongitudinally.
 7. An apparatus for equalizing the air pressure in aturbine engine air inlet comprising: a) a modulating plenum locatedadjacent to and surrounding the turbine engine air inlet wherein themodulating plenum is filled with air; b) an air pressure regulatorcoupled to the modulating plenum for regulating air pressure in themodulating plenum; c) an air pressure monitoring device coupled to themodulating plenum for monitoring the air pressure in the modulatingplenum; d) a permissive air flow divider located between the modulatingplenum and the turbine engine air inlet for defining an air flow regionin the modulating plenum and an air flow region in the turbine engineair inlet wherein the air flow divider permits air flow between the airflow regions and includes a plurality of perforations, where at leastone of said perforations is canted longitudinally and said perforationsare circumferentially spaced about a longitudinal axis of said plenumthus forming at least one ring of perforations; and e) an air pressuremaintenance system coupled to the modulating plenum for maintaining theair pressure in the modulating plenum at a determined pressure.
 8. Theapparatus of claim 7 wherein at least one ring of perforations is cantedlongitudinally.
 9. The apparatus of claim 8 wherein all rings ofperforations are canted longitudinally.
 10. An apparatus for equalizingthe air pressure in a turbine engine air inlet comprising: a) amodulating plenum located adjacent to and surrounding the turbine engineair inlet wherein the modulating plenum is filled with air; b) an airpressure regulator coupled to the modulating plenum for regulating airpressure in the modulating plenum; c) an air pressure monitoring devicecoupled to the modulating plenum for monitoring the air pressure in themodulating plenum; d) a permissive air flow divider located between themodulating plenum and the turbine engine air inlet for defining an airflow region in the modulating plenum and an air flow region in theturbine engine air inlet wherein the air flow divider permits air flowbetween the air flow regions and includes a plurality of perforations,where at least one of said perforation is canted radially and saidperforations are circumferentially spaced about a longitudinal axis ofsaid plenum thus forming at least one ring of perforations; and e) anair pressure maintenance system coupled to the modulating plenum formaintaining the air pressure in the modulating plenum at a determinedpressure.
 11. The apparatus of claim 10 wherein at least one ring ofperforations is canted radially.
 12. The apparatus of claim 11 whereinall rings of perforations are canted radially.